Secrecy Analysis of Modify-and-Forward Relaying With Relay Selection

This paper investigates the physical-layer security of the modify-and-forward (MF) protocol in multi-relay and multieavesdropper networks. Three relay selection critera are developed according to the channel state information (CSI) acquisition. CriterionI requires the CSI of all main channels for relay selection. Criteria II and III rely only on the CSI of the source-relay and relay-destination channels, respectively. We derive the exact secrecy outage probability (SOP), probability of nonzero secrecy capacity, and the ergodic secrecy rate in the closed forms. The €-outage secrecy capacity is also evaluated. Asymptotic analysis of the SOP explicitly reveals that the secrecy diversity order of criterionI depends on the total number of relays, whereas those of criteriaII and III are 2 and 1, respectively. The probability of nonzero secrecy capacity asymptotically decreases with the SNR of the wiretap channel as the eavesdropper is close to the source and relays. CriterionI is always superior to criteriaII and III in terms of the ergodic secrecy rate and €-outage secrecy capacity. Simulations results also demonstrated that the €-outage secrecy capacity deteriorates as the SNR of the eavesdropper's channel increases.